1. Field of the Invention
This invention relates generally to viscosity index (VI) improvers and, more particularly, to VI improvers which also exhibit favorable dispersant and antioxidant properties.
2. Description of the Background Art
The art contains many disclosures on the use of polymer additives in lubricating oil compositions. Ethylene-propylene copolymers and ethylene alpha-olefin non-conjugated diene terpolymers which have been further derivatized to provide bifunctional properties in lubricating oil compositions illustrate this type of oil additive.
U.S. Pat. No. 3,522,180 describes a method for the preparation of an ethylene-propylene copolymer substrate effective as a viscosity index improver for lubricating oils.
U.S. Pat. No. 4,026,809 describes grafted copolymers of a methacrylate ester and an ethylene-propylene-alkylidene norbornene terpolymer as a viscosity index improver for lubricating oils.
U.S. Pat. No. 4,032,700 describes a process for preparing aminated polymers which includes halogenating a copolymer of ethylene, a C.sub.3 to C.sub.18 a straight or branched chain alpha-chain olefin and a C.sub.5 to C.sub.14 acyclic or alicyclic non-conjugated diolefin and thereafter reacting said copolymer with a simple amine. The additives so produced are described as dispersants for hydrocarbon fuels or lubricants and as multifunctional dispersant-viscosity index improvers for lubricants. There is neither any express or implied recognition of using the particular amines described below to prepare the multifunctional VI improvers of this invention, nor is there any recognition of the antioxidant properties exhibited by the VI improvers of this invention.
U.S. Pat. No. 4,089,794 describes substantially saturated polymers comprising ethylene and one or more C.sub.3 to C.sub.28 alpha-olefins which have been solution-grafted in the presence of a free-radical initiator with an ethylenically-unsaturated carboxylic acid material at an elevated temperature, preferably in an inert atmosphere, and thereafter reacted with a polyfunctional material reactive with carboxy groups, such as (a) a polyamine, (b) a polyol, or (c) a hydroxyamine or mixtures thereof, to form polymeric reaction products. The reaction products are described as sludge-dispersing additives for hydrocarbon fuels and lubricating oils.
U.S. Pat. No. 4,137,185 describes a stabilized imide graft of an ethylene copolymer additive for lubricants.
U.S. Pat. No. 4,144,181 describes polymer additives for fuels and lubricants comprising a grafted ethylene copolymer reacted with a polyamine, polyol or hydroxyamine and finally reacted with a alkaryl sulfonic acid.
U.S. Pat. No. 4,146,489 describes a grafted copolymer where the backbone polymer is an oil-soluble ethylene-propylene copolymer or an ethylene-propylene-diene modified terpolymer with a graft monomer of C-vinylpyridine or N-vinylpyrrolidone to provide a dispersantVI improver for lubricating oils.
U.S. Pat. No. 4,320,019 describes a multipurpose lubricating additive prepared by the reaction of an interpolymer of ethylene and a C.sub.3 to C.sub.8 alpha-monoolefin with an olefinic carboxylic acid acylating agent to form an acylating reaction intermediate which is then reacted with an amine.
U.S. Pat. No. 4,340,689 describes a process for grafting a functional organic group onto an ethylene copolymer of an ethylene-propylene-diene terpolymer.
U.S. Pat. No. 4,357,250 describes a reaction product of a copolymer and an olefin carboxylic acid via the "ene" reaction followed by a reaction with a monoamine-polyamine mixture.
U.S. Pat. No.4,382,007 describes a dispersant - VI improver prepared by reacting a polyamine-derived dispersant with an oxidized ethylene-propylene polymer or an ethylene-propylene diene-terpolymer.
U.S. Pat. No. 4,698,169 describes a product made by reacting an alkenylsuccinic compound with an arylamine and an alkanolamine, an aminomethane or a hindered alcohol. The product is reported as providing dispersant and antioxidant activity to lubricant compositions when incorporated therein.
Commonly owned U.S. Pat. No. 4,863,623 describes an additive comprising an ethylene copolymer or terpolymer of a C.sub.3 to C.sub.10 alpha-monoolefin and optionally a non-conjugated diene or triene on which has been grafted an ethylenically unsaturated carboxylic function which is then further derivatized with certain amino-aromatic polyamine compounds.
It is, therefore, our understanding that the multifunctional viscosity index improver of this invention, which also exhibits favorable antioxidant properties because it includes the particular amines described below, has heretofore been unavailable.